Human erythrocyte phosphofructokinase has been purified to homogeneity. We will elucidate physicochemical structure including the molecular weights of the enzyme and its subunits, identity of the subunits and amino acid composition. We will study allosteric properties of the enzyme especially the mechanism of activation of the enzyme by sugar-bisP. Effect of hormone such as glucagon and insulin in a possible control of the futile cycle between fructose-6-P:fructose-bisP. We plan to see if phosphorylation-dephosphorylation of the enzymes may be involved in the control of the cycle by glucagon. Other factors including a metabolite in the regulation of this cycle will be investigated. Possible changes in phosphofructokinase, fructose-bisphosphatase and pyruvate kinase during different metabolic states of rats will be investigated. These metabolic states include starvation, diabetes and under hormonal treatment.